Setting the skill. One moment.
24 skills · 112 min
Skills
Skill 15 of 24
Turn on Cache Components in a Next.js app and resolve the blocking routes it surfaces.
20 minutes · 4,356 words · 18 sections
Install
npx skills add vercel/next.js --skill next-cache-components-adoptionnpx skills add vercel/next.js/plugin marketplace add vercel/next.jsThe first command installs just this skill, by the name in its SKILL.md; the second installs the whole repository.
Enable Cache Components on an app and walk it to a passing build. This skill sequences the work; per-error recipes live in the dev overlay fix cards and the build’s terminal output. The migrating to Cache Components guide (opens in a new tab) is the canonical reference for the concepts and per-API recipes this skill applies — consult it whenever the skill steps reference a pattern ("use cache", cacheLife, <Suspense> placement, etc.) and you want the full explanation.
App Router project. Cache Components is an App Router feature; cacheComponents: true does nothing for pages/ routes. If the project has a pages/ or src/pages/ tree but no app/ or src/app/ tree, stop and tell the user — Pages → App migration is its own project, not part of this skill. A hybrid app (both pages/ and app/) is fine: the flag affects the app/ routes; pages/ routes are unaffected and don’t need opt-outs.
A resolved app directory. Locate next.config.{js,ts,mjs,cjs} first: that’s the project root, and an agent invoked from a subdirectory would otherwise test for app/ against the wrong cwd and find nothing. Look for app/ and src/app/ under it, and treat every command and glob in this skill as relative to whichever one exists. If both exist, Next.js builds app/ and never looks at src/app/, so its routes are shadowed and unbuilt — tell the user that and ask which tree to migrate instead of picking one.
A runnable app. The whole loop verifies against next dev and a browser, so the app has to boot. If it reads a database or required env at import (e.g. an env.ts that throws on a missing DATABASE_URL), confirm it actually starts — with the real environment, or local data you stand up — before step 1. Adoption can’t be verified against an app that won’t run.
Next.js 16.3 or later. That release is where the pieces this skill relies on land: top-level cacheComponents, export const instant, the dev-overlay instant-navigation validation warnings, and the cache-components-instant-false codemod. If next --version reports below 16.3, upgrade first:
npx @next/codemod@latest upgrade latest to apply the version-to-version codemods.No passing baseline before the flag. If the app already uses "use cache", the pre-flag build errors with please enable the feature flag cacheComponents. Enabling the flag is the first thing you do (in Incremental, before the codemod; in Direct, before fixing routes) — not a thing to do after getting a passing build. Note this in your starting summary so it doesn’t read as a regression.
Offline docs. Guide links have offline copies under node_modules/next/dist/docs/ (bundled since Next.js 16.2), with the directory layout numbered for ordering (e.g. node_modules/next/dist/docs/01-app/02-guides/migrating-to-cache-components.md). If you can’t predict the numbered prefix, find node_modules/next/dist/docs -name '<slug>.md' resolves it. The /docs/messages/* error pages are not bundled.
Older versions without bundled docs. Suggest npx @next/codemod@latest agents-md to the user before starting: it downloads a version-matched copy to .next-docs/ and writes an index into AGENTS.md / CLAUDE.md. It touches files in their repo, so ask first and run it only if they want it.
There’s one loop: walk the route tree top-down, one feature at a time, adopting each route against next dev + a browser. The build is a final check for each feature, not the working surface.
The choice in step 1 is whether to opt every route out of validation first or fix routes as you go. Either way the loop is the same:
revalidate/dynamic/fetchCache exports), the build passes; you ship that as its own PR and then start the loop — removing one opt-out at a time and adopting that route. This splits the work into small, reviewable PRs.cacheComponents and start the loop on whatever the build flags first. Same loop, but every fix sits on one branch until adoption is complete.In both, the per-route success bar is the same: dev loop reports no errors AND next build passes. Check in with the user after every feature, and suggest a commit but never make one without their confirmation. Expect to spend most of the time in the loop, not in the pre-step.
cacheComponents: true requires every route to be prerenderable. A route that reads request-time data outside <Suspense> is “blocking” and fails the build. export const instant = false marks a route as allowed to block, which clears it in both dev and build; on a layout it covers the whole subtree during the build, but client navigations still validate each descendant segment on its own. Reads wrapped in a "use cache" (opens in a new tab) function count as cache boundaries, not blocking reads.
Three classes of blocker come up, usually in this order:
cookies(), headers(), await params, await searchParams). All four block when awaited at the top of a page or layout. params and searchParams often get missed because they’re not framed as “request data” the way cookies and headers are. The fix is to push the read into a <Suspense>-wrapped child — and for params/searchParams, forward the promise into the child and await it there; don’t await at the page top.new Date(), Date.now(), Math.random(), crypto.randomUUID()). These fail the build even with instant = false — the opt-out doesn’t suppress them. If they’re in a shared layout, they block every route under it. The codemod can’t fix them; after running it, use the build errors to identify which calls to translate by hand (see the incremental pre-step)."use cache" files that read request data. A file with a top-level "use cache" directive can’t export instant; combining the two errors with Only async functions are allowed to be exported in a "use cache" file., which means the directive was wrong for that route. Remove it before running the codemod.Prefer next dev over next build while you work.
next dev — the working surface. Visit a route; its blocking errors surface in the dev overlay with full stack traces and fix cards linking the per-error docs. Work one route at a time — errors don’t accumulate in one place. The route itself still returns HTTP 200, so read the overlay (or .next-dev.log), not status codes. A cleared overlay is one half of calling a route clean — the other half is browser verification (see step 2) and a passing build for that route.next build — detection only. The build is next dev‘s authoritative check, not its replacement. Use it as the last gate on each feature in the loop (a passing build is part of the per-route success bar) and as the final verification across the whole app. In Incremental, the build also confirms the pre-step (codemod opted every route out, no shared layout still has a sync-IO blocker) before you ship that PR. Don’t reach for the build instead of the dev loop while you’re working a route — a passing compile doesn’t tell you what ended up in the static shell and what streamed. By default the build stops at the first blocking route, so it’s also poor for sizing the work. Two flags help when iterating: --debug-build-paths builds only the routes you name (comma-separated glob patterns of file paths relative to the project root, e.g. --debug-build-paths="app/admin/**/page.tsx" — not URL paths; --debug-build-paths="app/(marketing)/about/page.tsx" — not /about; --debug-build-paths="app/admin" matches nothing and silently builds zero routes), and --debug-prerender disables the early exit so the build continues past the first prerender failure, reports every blocking route, and prints a fuller stack trace that names the originating file and line.Every blocking error has a docs page — open it. Both the dev overlay and the build terminal print a https://nextjs.org/docs/messages/<slug> link with each error. That page is the canonical recipe for the fix; the inline message is a summary. Fetch the link for every distinct error you encounter, even if you think you know the pattern — the recipes evolve, and the same error class can have different correct fixes depending on what the route reads. Don’t improvise from the inline message alone. (/docs/messages/* pages aren’t bundled offline; if you have no network, fall back to the per-API guides under node_modules/next/dist/docs/ and note the limitation when you report back.)
A passing build or a cleared overlay isn’t proof the route actually behaves — Cache Components is a runtime concern (a static shell with streamed data). Verify after every fix, not only at the end.
In preference order:
next-dev-loop (opens in a new tab) — strongly preferred. Cross-checks /_next/mcp against the live browser via agent-browser and surfaces both compile and runtime issues in one pass. The diagnostics (React tree, suspense boundaries, console + network) are richer than poking at next dev by hand.
Install it before starting the loop. Don’t wait until you hit something next dev alone can’t explain. It ships alongside this skill, so check whether it is already available first, and install it only if it is not:
npx skills add https://github.com/vercel/next.js/tree/canary/skills/next-dev-loopThe skill states its required agent-browser version and walks you through it.
Requires Turbopack. If package.json‘s dev script passes --webpack, flag it to the user and ask whether there’s a reason to stay on webpack. If not, switch to Turbopack (the Next.js 16.3+ default). If they want to keep webpack, skip this install and use the build-only loop instead.
You don’t need permission to install next-dev-loop itself. It’s a tool, like installing a dev dependency. If a user is present, briefly tell them you’re installing it for verification. In a non-interactive run (CI, dashboard, sandbox), install it without asking — “can’t prompt the user” is not a reason to skip. The only legitimate skip is a real technical blocker: no network, no npm, read-only filesystem, a stated no-new-deps policy, or a webpack-only dev script. If you skip, name the specific blocker in your final report.
A browser you can drive yourself. Playwright, agent-browser directly, any browser-automation tool. Use only when is genuinely blocked. You’ll miss the framework-side checks (), so DOM assertions alone don’t catch every regression — be more cautious about what you call “verified.”
Ask the user, in terms of the PRs they want, not the size of the job. Never use the internal labels (Incremental, Direct) when talking to the user — those are your own scaffolding. Ask in terms of PRs and features, e.g.: “Do you want me to first open a PR that turns on Cache Components and opts every route out of validation, then handle the actual route adoptions feature-by-feature in follow-up PRs? Or do everything on one branch?” Even on a tiny app, the incremental path still has value (review-sized PR, revertible, the // TODO: Cache Components adoption markers double as your work queue for next session). Don’t pick on their behalf.
If there’s no user to ask, default to Incremental and document the choice.
cacheComponents and go straight to step 2’s loop; the build’s blocking routes are the work queue.Before invoking the codemod, fix the blocker that does not require build feedback.
^export const (revalidate|dynamic|fetchCache) across the app directory and translate per the requires note above. The codemod does not touch them; leaving them in place fails the build after the codemod.The codemod refuses to run on a dirty working tree. Commit or stash unrelated work first, or pass --force to let its edits land alongside your WIP. Common false positive: if you recently upgraded Next.js, package.json and the lockfile will already be dirty — commit those first.
npx @next/codemod@latest cache-components-instant-false ./appPass the app directory you resolved in requires. A wrong path is not an error: it reports 0 ok and exits 0, so read the file count and treat zero as a failed run, not an adopted app.
Inserts export const instant = false (with a // TODO: Cache Components adoption comment) into every {page,layout,default} file under that directory, skipping files that already declare instant and any module marked "use client" or "use server". Then set cacheComponents: true. The TODO comments are the work queue for the loop.
If the codemod isn’t available (older @next/codemod, sandboxed environment, offline run), reproduce it by hand: for every {page,layout,default}.{js,jsx,ts,tsx} in the app directory that isn’t "use client" or "use server" and doesn’t already declare instant, insert this after the imports:
// TODO: Cache Components adoption. Refactor this route so this opt-out can be removed.
// See: https://nextjs.org/docs/app/guides/migrating-to-cache-components
export const instant = falseThe codemod opts every segment out, not only the root, on purpose. Resolution is top-down, first-explicit-config-wins: the highest instant = false decides the whole subtree. With an opt-out on every segment, removing one segment’s opt-out validates only that segment; descendants keep their own opt-outs and stay passing. If only the root were opted out, removing it would re-arm validation for the entire app at once.
Because the highest opt-out wins, remove them top-down (root layout first, then descend). Removing a leaf’s opt-out does nothing while an ancestor still holds one.
Next, run next build to surface blockers the codemod could not handle. The build is the proof, not the codemod run — a shared layout that calls new Date() / Math.random() directly still fails regardless of the opt-out (see background). If the normal build reports a sync-IO error without locating the call, rerun that route with next build --debug-prerender --debug-build-paths="app/path/to/page.tsx". For each sync-IO error it reports:
Sync-IO at module/render time. Use the route, originating file and line, and /docs/messages/ link in the build output to locate the error. If needed, grep the whole repo for new Date(), Date.now(), Math.random(), and crypto.randomUUID() (not only app/**/layout.{js,jsx,ts,tsx} — the read might live in any component imported by a layout). Do not change unreported matches. Unblock the reported call with the await connection() + <Suspense> fix from its blocking-prerender-* error card: it defers the value to request time, exactly as it behaved before the migration, so it needs no product decision. Add this exact comment on the line above the await connection():
// TODO: Cache Components adoption. Added to unblock the build: remove this connection() to re-trigger the error and review the fix options.It shares the TODO: Cache Components adoption prefix with the comments the codemod writes, so the check-in grep finds both. Removing the await connection() makes the error fire again with its fix cards — the same motion as removing an opt-out in the loop.
After each fix, rerun the scoped build when available, then run next build again to find the next blocker. Repeat until the normal build passes.
After the build passes, confirm the root layout got an opt-out (grep -n "export const instant" <app dir>/layout.*). The root layout renders every route, including framework routes like /_not-found, so if it was missed, add export const instant = false to it by hand.
Synthetic routes like /_not-found have no user file — when they block, fix the root layout’s opt-out, not the synthetic route. Client Components ("use client") get no opt-out (it’s a build error to export instant from them), but they are not a rare blocker. The high-frequency case is a client component in the root layout’s nav or header calling usePathname()/useSearchParams(): it blocks every dynamic route with blocking-prerender-client-hook, and static routes pass (the pathname is known at prerender), which masks it until you reach a dynamic segment. It’s not an ancestor-data fix — follow the error’s docs page (opens in a new tab) for the <Suspense> recipe. Only when a client route blocks on server data do you fix that data in its ancestor.
Incremental only. Stop here before starting step 2 — the pre-step is the shippable PR. Talk to the user in their language; don’t say “Incremental” or other internal labels; talk about adoption, PRs, and what the app does now. Tell them:
instant = false with a // TODO: Cache Components adoption comment, except client components and any that already had an instant export.Moving to step 2 without checking in defeats the point of taking the incremental path.
Set cacheComponents: true and move to step 2. The build’s blocking routes are the work queue.
A “feature” is a single product surface — app/settings/profile/**, app/posts/[slug]/** — not a whole top-level app like app/dashboard/**. Finish one end-to-end before starting the next.
Within a feature, walk top-down (layouts before pages, root layout first). Removing a layout’s opt-out before its descendants exposes the layout’s own blocking reads. (Direct: there are no opt-outs to remove — fix each failing route; if a hand-written opt-out on an ancestor shadows it, remove that first.)
A passing build mid-walk doesn’t mean the layout is clean. Removing a layout’s opt-out while its descendant pages still have theirs keeps the build passing — each page shadows the inherited validation. The layout’s actual blocking reads only surface once nothing below it shadows them. Don’t call a feature done at the layout boundary.
Use the with-a-browser loop unless a browser is genuinely unreachable. The next-dev-loop skill is the source of truth for what counts as “browser available” and how to install it.
Per route:
https://nextjs.org/docs/messages/<slug>), apply the recipe from there. The inline overlay text is a summary; the docs page is the source of truth.Used when there’s no way to drive a browser — CI, sandbox, the user has no next dev running and you can’t start one. Weaker signal: confirms the build passes and the route prerenders, but not what ended up in the static shell vs streamed.
Per route:
--debug-build-paths app/<route>/** (only that route) or --debug-prerender (full build, but past the first failure). Route passing? Move on. Still blocking? Fix.https://nextjs.org/docs/messages/<slug>), apply the recipe from there.◐ route still needs a browser pass before the feature is done.getThing(id)) doesn’t clear an await params at the top of the page body — push the param promise into the <Suspense>-wrapped child.next-dev-loop session runs the browser headed, so drive to the page and leave it on screen so the user is looking at the thing they’re deciding about, with a screenshot as the fallback when a headed browser isn’t possible. “Should this stay blocking?” is much easier to answer while looking at the page than at a file path.// TODO: Cache Components adoption on opt-outs, and the user’s existing comments. Don’t annotate every <Suspense> boundary or "use cache" call with what it does — the code says that. Drop a comment only when the why isn’t clear from the code (e.g. a deliberate Block with a reason).Keep a todo list of the feature’s routes. When every route in the feature is clean, move to step 3.
Checklist before checking in with the user:
next build completes without blocking-route errors.grep -rn "TODO: Cache Components adoption" finds both the codemod’s opt-out comments and the sync-IO unblocks from the pre-step. Any instant = false left behind is a deliberate, documented Block — comment rewritten to a reason (see references/per-page-decisions.md (opens in a new tab) → “when to leave a Block in place”). Any await connection() left behind has been reviewed and kept on purpose, not left over from the pre-step.<Suspense> fallback resolves to its real content. Capture both states if you can — the fallback (mid-stream) and the final paint — so you have a streaming-experience demo to show the user. Throttle the network in the browser if streaming is too fast to observe.Then check in with the user. Same rule as the pre-step: speak their language. Don’t say “feature-by-feature loop” or other internal labels; talk about the feature you adopted and what the user will see.
next-dev-loop session runs the browser headed, so drive the route live for the user so they see the static shell → fallback → final content sequence in real time. If you can’t drive a live browser, attach the before/after screenshots you captured instead.Trivial features can skip the check-in. If adopting a feature only meant removing its // TODO: Cache Components adoption opt-out (no <Suspense> added, no 'use cache' introduced, no render order change), the user sees nothing different. Move on to the next feature without stopping; mention it in passing the next time you do check in.
When the loop has run on every feature — every remaining instant = false sits under a reason comment, grep -rln "TODO: Cache Components adoption" app returns nothing — point the user at further reading if they want to push the experience further, or stop and ship.
ƒ → ◐ is where adoption usually lands. ◐ (Partial Prerender) means a static shell prerenders and the request-time content streams in — the goal state for any route that reads cookies(), headers(), params, or searchParams. Some routes legitimately stay ƒ when they do request-time work through a documented escape hatch (e.g. a layout that uses await connection()); the page is no longer opted out, it’s genuinely dynamic. Don’t remove the escape hatch only to chase a ◐. The inverse holds: instant = false does not force a route to be ƒ. The glyph reflects what the route does at prerender time, not which validation knobs it exports.
◐ tells you a shell exists, not what’s in it. A <Suspense> boundary placed too high (e.g. wrapping the entire page body, or <Suspense fallback={null}> around the article content) pushes the visible content out of the static shell into the streamed payload; the build still reports ◐ because some shell prerendered (often only <html><body> with framework markup). The route table can’t tell you what’s in the shell; a browser can. If the shell is empty and everything streams, pull the <Suspense> boundary down closer to the actual dynamic read.
The work below is optional and lives in the docs — link the user to them and let them decide which to take on next. Don’t walk these through inside this skill.
next-partial-prefetching-adoption (opens in a new tab) — the follow-up skill that adopts Partial Prefetching: it enables partialPrefetching and audits every <Link prefetch={true}> against a decision table (or adopts incrementally with the flag off, driven by the instant-link-prefetch-partial insight). It sequences this the same way this skill sequences Cache Components, but the insights are dev-only, so it’s a browser click-through, not a build loop. Recommended after instant navigation, since those fixes feed directly into how much of each route the shell can prefetch. Concepts live in the Adopting Partial Prefetching guide.Turn on Cache Components in a Next.js app and resolve the blocking routes it surfaces. Use when the user wants to enable, adopt, or migrate to Cache Components, flip the `cacheComponents` flag, work through a flood of blocking-prerender / instant validation errors, run the `cache-components-instant-false` codemod, or decide between opting routes out with `export const instant = false` and fixing them in place.
The verbatim description from this skill’s front matter — the string an agent matches on to decide whether to load it.
canary, last pushed 28 August 2026.SKILL.md, not by matching a directory convention. 2 distinct layouts observed: .agents/skills/*/SKILL.md, skills/*/SKILL.md.h1 and no skipped levels:.claude-plugin/marketplace.json by Vercel, declaring 1 plugin. It is read for editorial metadata only — never as the skill index, which is always the repository tree.No incompatible config keys. cacheComponents: true errors on any file that still exports dynamic, revalidate, or fetchCache. Translate, don’t delete. Each export encodes behavior the route needs to keep doing; migrate each one to its Cache Components equivalent via the migration guide’s per-key sections (opens in a new tab). The exception is dynamic = 'force-dynamic': under Cache Components every route is already dynamic by default, so the migration guide removes it outright rather than translating it — don’t overthink a batch of identical force-dynamic deletions. revalidate and fetchCache still need real translation. If a value can’t be cleanly translated yet, leave a // TODO: Cache Components adoption — restore revalidate = 3600 comment so the loop picks it up. The cache-components-instant-false codemod does not touch these.
experimental.dynamicIO is fatal. It was renamed to top-level cacheComponents and the old key now aborts before any build can run — remove it (or replace with cacheComponents: true) first. experimental.useCache is still accepted as a deprecated alias; redundant once cacheComponents: true is set, so remove it for clarity.
next-dev-loop/_next/mcpBuild-only. If you can’t run a dev server at all, the build is your only signal. ○ (Static) routes with no <Suspense> are fully verified by the build (nothing streamed to test). ◐ (Partial Prerender) routes are only shell-verified — flag them when you report back.
No tooling at all. Ask the user to run the dev server (or build) and report what they see, or hand off the milestone you’ve reached.
@next/playwright instant() (opens in a new tab) helper asserts on the UI that’s available immediately on navigation, so regressions surface in CI. Recommend it once a route is instant: next-dev-loop confirms it now; an instant() test keeps it that way.next-cache-components-optimizer (opens in a new tab) — a separate skill that grows each route’s static shell so more of the page prerenders and less streams in. Pure optimization, not part of adoption./vercel/next.js.md, and each skill at its own .md URL.2 files · 7 KB
Everything this skill ships beside its prose. All of it is set here, as subchapters of skill 15.
Documentation the agent loads on demand, rather than up front.